You should have all these qualities that base in the Bible which listed below to be a preacher. If not, you can still practice them all for you to understand the Bible much better cause not all man can understand it, because it said in Mark 4:11-12 of the Bible, “When Christ was alone, they that were about him with the twelve asked of him the parable. And he said unto them, 'Unto you it is given to know the mystery of the kingdom of God, but unto them that are without, all these things are done in parables, that seeing they may see and not perceive, and hearing they may hear and not understand...'”
Turn at the reproof of God to know His words because He said according in the book of Proverbs 1:23, “Turn you at my reproof, behold, I will pour out my spirit unto you, I will make known my words unto you.”
You should be wise and not a wicked to understand the words because according in Daniel 12:9-10, “The words are closed up and sealed till many shall be purified, made white, and tried in the time of the end, but the wicked shall do wickedly and none of the wicked shall understand, but the wise shall understand.”
You must worship the God, so He can open your heart because there's a happening like that in Acts 16:14, “A certain woman named Lydia a seller of purple, of the city of Thyatira, which worshipped God, heard us, whose heart the Lord opened, that she attended unto the things which were spoken of Paul.”
You must know the mind of Christ because in 1 Corinthians 2:9-16, “The things that not seen nor heard, neither have entered into the heart of man, which God had prepared for them that love him. But God had revealed them unto us by his Spirit, for the Spirit searched the deep things of God. The things of God are known by the Spirit of God. Now we have received the spirit which is of God, that we might know these things. We speak in the words which the Holy Ghost had teach. He that is spiritual judged all things. For who had known the mind of the Lord, that he may instruct him? But we have the mind of Christ.”
You must be a believer of the gospel of the salvation to get a Holy Spirit because in Ephesians 1:13, “In whom you also trusted, after that you heard the word of truth, the gospel of your salvation, in whom also after that you believed, you were sealed with that holy Spirit of promise...”
Those qualities that listed above are important for preaching the written word of God which is in the Bible. Remember, the apostles had preached the kingdom of heaven by the guidance of the Holy Spirit, also known as the Holy Ghost.